These rocks form under the action of pressure, volume and temperature (PVT) changes.

Identify the correct statements:

a. 1 only

b. 2 only

c. All are correct

d. None

Q18. The process of converting unconsolidated sediments into sedimentary rocks requires which of the following

Compaction

Re-crystallisation

Cementation

Weathering

Select the correct answer using the codes given below

a. 1 and 2

b. 2 and 3

c. 1, 2 and 3

d. All of these

Q19. The process of metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called

a. Foliation or lineation.

b. Banding

c. Both a and b

d. None of the above

Q20. Pyroxene consists of

a. calcium, aluminum

b. magnesium, iron

c. silica

d. all the above

1.B

Many scientists thought of this similarity and considered the possibility of the two Americas, Europe and Africa, to be once joined together. From the known records of the history of science, it was Abraham Ortelius, a Dutch map maker, who first proposed such a possibility as early as 1596.

2.B

Wegener suggested that the movement responsible for the drifting of the continents was caused by pole-fleeing force and tidal force. The polar-fleeing force relates to the rotation of the earth.

3.D

The major plates are as follows :

Antarctica and the surrounding oceanic plate

North American (with western Atlantic floor separated from the South American plate along the Caribbean islands) plate

South American (with western Atlantic floor separated from the North American plate along the Caribbean islands) plate

Pacific plate

India-Australia-New Zealand plate

Africa with the eastern Atlantic floor plate

Eurasia and the adjacent oceanic plate.

Some important minor plates are listed below:

Cocos plate : Between Central America and Pacific plate

Nazca plate : Between South America and Pacific plate

Arabian plate : Mostly the Saudi Arabian landmass

Philippine plate : Between the Asiatic and Pacific plate

Caroline plate : Between the Philippine and Indian plate (North of New Guinea)

Fuji plate : North-east of Australia.

4.A

Alfred Wegener—a German meteorologist who put forth a comprehensive argument in the form of “the continental drift theory” in 1912. This was regarding the distribution of the oceans and the continents. According to Wegener, all the continents formed a single continental mass, a mega ocean surrounded by the same. The super continent was named PANGAEA, which meant all earth. The mega-ocean was called PANTHALASSA, meaning all water

5.C

6.A.

The ocean floor may be segmented into three major divisions based on the depth as well as the forms of relief. These divisions are continental margins, deep-sea basins and mid-ocean ridges.

Continental Margins: These form the transition between continental shores and deep-sea basins. They include continental shelf, continental slope, continental rise and deep-oceanic trenches.

7.C

A tectonic plate (also called lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.

The theory of plate tectonics proposes that the earth’s lithosphere is divided into seven major and some minor plates.

The slow movement of hot, softened mantle that lies below the rigid plates is the driving force behind the plate movement.

8.B

Some important minor plates are listed below:

Cocos plate : Between Central America and Pacific plate

Nazca plate : Between South America and Pacific plate

Arabian plate : Mostly the Saudi Arabian landmass

Philippine plate : Between the Asiatic and Pacific plate

Caroline plate : Between the Philippine and Indian plate (North of New Guinea)

Fuji plate : North-east of Australia.

9.C

Divergent Boundaries Where new crust is generated as the plates pull away from each other. The sites where the plates move away from each other are called spreading sites.

Convergent Boundaries

Where the crust is destroyed as one plate dived under another. The location where sinking of a plate occurs is called a subduction zone.

Transform Boundaries

Where the crust is neither produced nor destroyed as the plates slide horizontally past each other. Transform faults are the planes of separation generally perpendicular to the midoceanic ridges.

10.B

Quartz: It is one of the most important components of sand and granite. It consists of silica. It is a hard mineral virtually insoluble in water. It is white or colourless and used in radio and radar.

It is one of the most important components of granite.

11. A

Metamorphic Rocks: The word metamorphic means ‘change of form’. These rocks form under the action of pressure, volume and temperature (PVT) changes.

Metamorphism occurs when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks.

12.C

Mica: It comprises of potassium, aluminium, magnesium, iron, silica etc. It forms 4 per cent of the earth’s crust. It is commonly found in igneous and metamorphic rocks. It is used in electrical instruments.

13.C

14.D

15.C

Igneous Rocks: As igneous rocks form out of magma and lava from the interior of the earth, they are known as primary rocks.Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.

16.C

Sedimentary Rocks: The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling. Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification. In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification. Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.

17. C

Metamorphism occurs when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks.

Metamorphism is a process by which already consolidated rocks undergo recrystallisation and reorganisation of materials within original rocks.

18.C

The process, by which loose sediment is hardened to rock are collectively called Lithification.

Once this happens, continued erosion and re-transport of the sediments become much more difficult. The process, which involves in it are compaction, re-crystallization and cementation.

19.A

The process of metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation or lineation.

Sometimes minerals or materials of different groups are arranged into alternating thin to thick layers appearing in light and dark shades. Such a structure in metamorphic rocks is called banding and rocks displaying banding are called banded rocks.